Viral infections are a continuing medical problem because, like any rapidly-dividing infectious agent, there are continuing mutations that help some sub-populations of viruses resistant to current treatment regimens. Many virally-based diseases do not have effective anti-viral treatments, because such treatments address the symptoms of the viral disease and not the root cause of the disease.
Pertussis toxin (PTX) is a 105,700 Dalton polypeptide that has both an alpha subunit and a beta subunit (PTBS). Pertussis toxin (PTX), a heterohexameric protein released by Bordetella Pertussis, exhibits diverse biological activities, mediated mostly by the A-subunit (A-promoter) which inactivates signaling pathways of members of the G.sub.i -G.sub.0 and G.sub.t -protein family. Binding to the receptor and internalization of the toxin is mediated by the B-oligomer. The hexamer is composed of one S1 subunit having a molecular weight of 28 kDa, one S2 subunit having a molecular weight of 23 kDa, one S3 subunit having a molecular weight of 22 kDa, two S4 subunits having a molecular weight of 11.7 kDa, and one S5 subunit having a molecular weight of 9.3 kDa. The S1 examers constitute the active A promoter, and an oligomer composed of one each of the S2, S3, and S5 subunits plus two S4 subunits constitute the B-oligomer that is the binding region. (Ui, Pertussis Toxin as a Probe of Receptor Coupling to Inositol Lipid Metabolism. Phosphoinositides and Receptor Mechanism, pp 163-195. Alan R. Liss, Inc., 1986). In addition, the D1 oligomer is composed of one each of the S2 and S4 subunits and can bind to a p43 PTX receptor, and a D2-oligomer is composed of one each of the S3 and S4 subunits and can bind to a p70 PTX receptor (Wong and Rosoff "Pharmacology of Pertussis Toxin B" Can. J. Physiol. Pharmacol. 74:559-566, 1996).
The A-promoter is released from the holotoxin molecule as a result of an allosteric effect of intracellular ATP. Specifically, intracellular ATP binds to the S3 subunit of the B-oligomer. The active center of ADP-rybosil transferase, unmasked in the released A-promoter molecule, can interact with intracellular reduced glutathione, which cleavages disulfide bonds essential for enzymatic activity (Ui, Pertussis Toxin as a Probe of Receptor Coupling to Inositol Lipid Metabolism. Phosphoinositides and Receptor Mechanism, pp 163-195. Alan R. Liss, Inc., 1986). The A-subunit possesses adenine diphosphate (ADP) ribosyltransferase activity, which catalizes ADP-ribosylation of G-proteins, leading to their dissociation from receptors and uncoupling of corresponding signal transduction events. Due to this feature, PTX has become a very useful pharmacological tool for the identification of G proteins in the plasma membrane.
The B (binding) oligomer confers cell membrane-binding specificity by interacting with specific receptors. In lymphocytes, two PTX-binding proteins have been identified: a 43-kDa (Rogers et al., J. Immunol. 145:678-683, 1990) and a 70-kDa (Armstrong et al., Infect. Immun. 62:2236-2243, 1994) receptors. A leukocyte-specific integrin, Mac-1 (CD11b/CD18) may be a binding site for PTX on macrophages (Wong et al., Immunology 88:90-97, 1996). Occupation of these putative receptors by the B-oligomer can trigger phospholipase C (PLC) and tyrosine kinase-dependent signal transduction pathways. However, the effect of these events on the function of a target cell is not characterized, and pharmacological properties of the PTX B-oligomer are largely unknown. Nevertheless, the B-oligomer was shown to potentiate the immune response to intranasally administered influenza vaccine in mice when used as an adjuvant (Oka et al., Vaccine 12:1255-1258, 1994), and also induced resistance to lethal doses of mouse adenovirus infection (Winters et al., Dev. Biol. Stand. 61:233-240, 1985). The B-oligomer was shown to improve immune responses to viral vaccines, when used as an adjuvant (Oka et al., Vaccine 12:1255-1258, 1994; and Winters et al., Dev. Biol. Stand. 61:233-240, 1985).
In addition, whole Pertussis Toxin affected HIV replication in U1 cells (in vitro) wherein there was demonstrated a role of Gi protein PTX sensitivity in the U1 chronically infected monocytic cell line (Chowdury et al., Virology 203:378-383, 1994). In addition the stimulated PTX receptor can induce phospholipase C, which cuts off PIP.sub.2 and produces IP.sub.3 (inositol triphosphate) and DAG (diacyl glycerol) (Rosoff and Mohan, J. Immunol. 149:3191-3199, 1992). The PTX receptor further appears to require the coexpression of a CD3/TCR complex (Gray et al., J,. Immunol. 142:1631-1638, 1989). Moreover, concentrations of the beta subunit of PTX (100 nM) stimulated production of interleukin-2 (IL-2) with a similar pattern seen with the antibody OKT3 in vitro in Jurkat cells (Rosoff et al., J. Immunol. 139:2419-2423, 1987).
Anti-viral therapies directed against the virus (as opposed to directed to symptoms of the disease) have generally been based upon viral enzymatic inhibition, such as HIV therapies directed against viral reverse transcriptase or viral protease enzymes. Therefore, there is a need in the art to discover and develop new anti-viral therapies that are not based upon a mechanism of action to inhibit virus-specific enzyme that is used in viral replication.